Sharp pruning shears work good. Electric or gas powered hedge trimmers work very good also.
If you would first take the time to tie the grass into a "pony tail" tied with twine then cut below the twine cleanup will be much easier.

Miscanthus grasses can cause skin issues. I wear gloves and long sleeves plus long, heavy pants and solid shoes or boots when trimming them.
For a really big job I would tape my wrists to be sure my skin is well protected. The grass blades cause mechanical skin damage - they can slice the skin. Ouch.

Edited to add:
I probably should have also said that you can use a reciprocating say ( I would recommend using a cordless type to avoid accidentally cutting the power cord). There are some landscape companies that use a chain saw. I guess each person will find the best tool for the job.

I use gas hedge trimmers on mine to about 6 - 8 inches tall and then in early Spring before new growth burn off the remainder. This allows the new growth to come through without getting that big dead spot in the middle of the grass. Be careful and have water at the ready.